Biomechanical Energy Harvesting Research Articles

Kinetic Walking Energy Harvester Design for a Wearable Bowden Cable-Actuated Exoskeleton Robot.

Over the past few decades, wearable exoskeletons of various forms have been developed to assist human activities or for rehabilitation of movement disorders. However, sustainable exoskeletons with efficient energy harvesting devices still have not been fully explored. In this paper, we propose the design of a lightweight wearable Bowden-cable-actuated soft exoskeleton robot with energy harvesting capability. Unlike previous wearable exoskeletons, the presented exoskeleton uses an electromagnetic generator to both harvest biomechanical energy and to output mechanical torque by controlling an operation mode relay switch based on a human’s gait. Moreover, the energy-harvesting module also acts as a knee impact absorber for the human, where the effective damping level can be modulated in a controlled manner. The harvested energy is regulated and stored in super capacitors for powering wireless sensory devices when needed. The experimental results show an average of a 7.91% reduction in thigh muscle activity, with a maximum of 3.2 W of electric power being generated during movement downstairs. The proposed design offers important prospects for the realization of lightweight wearable exoskeletons with improved efficiency and long-term sustainability.

Antibacterial, Antifreezing, Stretchable, and Self‐Healing Organohydrogel Electrode Based Triboelectric Nanogenerator for Self‐Powered Biomechanical Sensing

AbstractFlexible and wearable electronic devices have broad applications in human–machine interaction and personal health monitoring. To meet different application scenarios, in this work, an antibacterial, antifreezing, stretchable, and self‐healing organohydrogel‐based triboelectric nanogenerator (O‐TENG) for biomechanical energy harvesting and self‐powered sensing is developed. Through integrating Ag nanoparticles on reduced graphene oxide sheets (Ag@rGO) into poly(vinyl alcohol)‐polyacrylamide (PVA‐PAAm) dual‐network organohydrogel with dynamic borate bonds, denoted as Ag@rGO/PVA‐PAAm, the organohydrogel has high conductivity, good stretchability, and antifreezing and self‐healing properties. When using Ag@rGO/PVA‐PAAm as the electrode layer of O‐TENG, it can effectively inhibit Gram‐negative bacterium E. coli and Gram‐positive bacterium S. aureus while showing high cytocompatibility. With the self‐healing and antifreezing property, the fabricated O‐TENG has stable output performance under room temperature and low temperature of −30 °C, even after Ag@rGO/PVA‐PAAm is damaged and self‐healed. This O‐TENG is demonstrated to harvest mechanical energy and is used as self‐powered sensors for recognizing handwriting and wrist motion state. This work provides a new pathway for design and application of multifunctional flexible wearable devices.

Cooperative compliant traction mechanism for human-friendly biomechanical energy harvesting

In this study, a human-friendly biomechanical energy harvester (HF-BEH) utilizing cooperative compliant traction mechanism is proposed. The knee joint is used to drive the harvester through a compliant medium without wearing any mechanical components. The driving force is large, and there is no added weight and restraint on the knee joint. The work of the harvester can naturally collaborate with the walking/running of the user due to the mechanical adaptability of the compliant medium and reasonable settings, that is, the harvester collects energy when the user does negative work. Frequency up-conversion and mechanical rectification are used to improve electromechanical conversion efficiency. A man wearing the HF-BEH prototype can generate an average power of 0.22 W while walking (4 Km/h) and 0.30 W when running (10 Km/h), with little impact on his mobility. The possibility of self-powered emergency call, positioning and tracking, health monitoring and physical therapy based on HF-BEH has been verified by powering commercial smart electronics with these functions. Human-vehicle interaction through self powered wireless sensing based on HF-BEH is demonstrated to improve the safety of people with limited responsiveness and mobility in the traffic environment. The proposed energy harvesting system can be integrated with functional modules as a self-powered human-assisted system.

Flexible Ionic Diodes with High Rectifying Ratio and Wide Temperature Tolerance

AbstractSoft iontronics expand the toolbox of bio‐integrated or bio‐interfaced devices, owing to their natural resemblance with living systems; however, the development for analogous integrated ionic circuits is immature due to the difficulty of fabricating fundamental ionic logic elements. Among these, ionic diodes have motivated great endeavors for their unique ionic current rectifying characteristics. Nonetheless, it is still challenging to achieve high‐performance ionic diodes; also, most reported aqueous solution‐based ionic diodes fail to work at extreme temperatures, seriously hindering their practical uses. This work reports a highly rectifying, temperature‐tolerant, and flexible hydrogel ionic diode enabled by an ethylene glycol/water binary solvent system. The ionic diodes exhibit outstanding dehydration resistance to high temperatures (100 °C) and anti‐freezing performance at low temperatures (−20 °C). Rectification ratios as high as 1201 (with 0% ethylene glycol content) and 566 (with 40% EG content) are achieved, which are distinctly advantageous over most previous reports. A flexible four‐diode bridge full‐wave rectifier circuit is then fabricated, and its integration with the triboelectric nanogenerator for effective biomechanical energy harvesting is demonstrated. This work is believed to open up new insights for the development of future bio‐interfaced applications.

Industrial production of bionic scales knitting fabric-based triboelectric nanogenerator for outdoor rescue and human protection

Obtaining inspirations from natural selection have promoted wearable electronics innovation and provided a broad prospect for smart textiles compatible with excellent biological characteristics. Combining bionic scales with knitted structure can satisfy the conflicting requirements of protection and flexibility, which is vital to the smart outdoor garment application. However, it is very difficult to integrate high-speed fabrication and intelligentization of the complex bionic structure and the fabric while maintaining the original flexibility, comfort, and breathability of the fabric as much as possible. Herein, a novel, one-time, high-speed V-bed flat knitting fully-formed technology is used to prepare a bionic scales knitting triboelectric generator (BSK-TENG) as a new kind of wearable fabric with both intelligence and function. When used outdoors, the BSK-TENG can harvest water-drop energy and biomechanical energy owing to its distinctive 3D hierarchy structure. Besides, a multifunctional and intelligent personal outdoor rescue system with wireless signal transmission is also designed and manufactured by using the BSK-TENG as a self-powered and wearable human-computer interaction sensing device. What’s more, due to the obvious anisotropy exhibited during bending, the BSK-TENG can be further used as joint supporting protection for outdoor sports. This mass-produced 3D BSK-TENG not only has great commercial potential, but also can provide a promising research direction for multifunctional wearable devices in energy harvesting, self-powered sensing and human health protection.

An Energy Harvester Coupled with a Triboelectric Mechanism and Electrostatic Mechanism for Biomechanical Energy Harvesting.

Energy-harvesting devices based on a single energy conversion mechanism generally have a low output and low conversion efficiency. To solve this problem, an energy harvester coupled with a triboelectric mechanism and electrostatic mechanism for biomechanical energy harvesting is presented. The output performances of the device coupled with a triboelectric mechanism and electrostatic mechanism were systematically studied through principle analysis, simulation, and experimental demonstration. Experiments showed that the output performance of the device was greatly improved by coupling the electrostatic induction mechanisms, and a sustainable and enhanced peak power of approximately 289 μW was produced when the external impedance was 100 MΩ, which gave over a 46-fold enhancement to the conventional single triboelectric conversion mechanism. Moreover, it showed higher resolution for motion states compared with the conventional triboelectric nanogenerator, and can precisely and constantly monitor and distinguish various motion states, including stepping, walking, running, and jumping. Furthermore, it can charge a capacitor of 10 μF to 3 V within 2 min and light up 16 LEDs. On this basis, a self-powered access control system, based on gait recognition, was successfully demonstrated. This work proposes a novel and cost-effective method for biomechanical energy harvesting, which provides a more convenient choice for human motion status monitoring and can be widely used in personnel identification systems.

Bistable energy harvesting backpack: Design, modeling, and experiments

Inspired by the dynamics of the noninertial systems, a novel bistable energy harvesting backpack is proposed that improves biomechanical energy harvesting performance. In contrast to traditional bistable energy harvesters that use an oblique compressed spring, a new bistable backpack is developed that uses the change of a spring torque direction located on a pinion. A detailed nondimensionalized model of the novel bistable energy harvesting backpack is developed and analyzed. Based on the dynamic bistable model, the influence of the carried backpack mass on the symmetry and the bifurcation frequency and amplitude of oscillation is examined to determine the ideal design parameters of the bistable backpack for experimental analysis and prototype manufacture. A comparison is made between the new bistable backpack and a traditional linear backpack under both harmonic and human walking excitation. The new bistable backpack design exhibits an improved frequency bandwidth from 1 Hz to 1.65 Hz at the base harmonic excitation of 2 m/s2 and the harvesting performance is enhanced from 2.34 W to 3.32 W when the walking speed is 5.6 km/h. The bench and treadmill tests verify the theoretical analysis and demonstrate the ability of the bistable energy harvesting backpack for broadband and performance enhancement.

Smart Textile Triboelectric Nanogenerators: Prospective Strategies for Improving Electricity Output Performance

By seamlessly integrating the wearing comfortability of textiles with the biomechanical energy harvesting function of a triboelectric nanogenerator (TENG), an emerging and advanced intelligent textile, i.e., smart textile TENG, is developed with remarkable abilities of autonomous power supply and self-powered sensing, which has great development prospects in the next-generation human-oriented wearable electronics. However, due to inadequate interface contact, insufficient electrification of materials, unavoidable air breakdown effect, output capacitance feature, and special textile structure, there are still several bottlenecks in the road towards the practical application of textile TENGs, including low output, high impedance, low integration, poor working durability, and so on. In this review, on the basis of mastering the existing theory of electricity generation mechanism of TENGs, some prospective strategies for improving the mechanical-to-electrical conversion performance of textile TENGs are systematically summarized and comprehensively discussed, including surface/interface physical treatments, atomic-scale chemical modification, structural optimization design, work environmental control, and integrated energy management. The advantages and disadvantages of each approach in output enhancement are further compared at the end of this review. It is hoped that this review can not only provide useful guidance for the research of textile TENGs to select optimization methods but also accelerate their large-scale practical process.

Large‐scale fabrication of core‐shell triboelectric braided fibers and power textiles for energy harvesting and plantar pressure monitoring

AbstractFlexible and wearable energy harvesting devices and multifunctional sensors have been widely reported, but challenges in the large‐scale manufacturing process still exist. This work reports a large‐scale fabrication method of core‐shell triboelectric braided fibers that exhibit stable structure and strong tensile strength, which can be further integrated into power textiles with different fabric structures, such as weaving and knitting, with the purpose of biomechanical energy harvesting or plantar pressure monitoring. The triboelectric braided fibers integrating on the knitting power textiles exhibit good pressure sensitivity and fatigue resistance, which is combined with traditional socks to measure the pressure distribution of the plantar in different positions. The weaving power textiles exhibit high electrical output, which can be used for biomechanical energy harvesting and can easily light up 116 commercial LEDs. This large‐scale preparation approach provides more possibilities for power textiles applications in self‐powered wearable electronics and human–computer interfacing.

Hybrid Nanogenerator for Biomechanical Energy Harvesting, Motion State Detection, and Pulse Sensing

AbstractHarvesting biomechanical energy to power wearable electronic devices shows great potential in the field of the Internet of Things. An insole hybrid nanogenerator (IHN) has been designed based on a combination of multilayered triboelectric nanogenerator and arched piezoelectric nanogenerator. The IHN not only can convert the mechanical energy of the footsteps into electricity, but also distinguishes three kinds of motion states: walking, stepping, and jumping. A maximum open‐circuit voltage of 150 V and a short‐circuit current of 4.5 µA are achieved from human body motions. After walking for 8 min, the IHN can charge a 100 μF capacitor to 2.5 V. Then, a self‐powered dorsalis pedis artery monitoring system is designed, which can detect the pulse signals of the dorsalis pedis artery in real‐time. The integrated design of energy collection, storage, and utilization has important application potential in future self‐powered monitoring of patients and intelligent analysis of blood supply to the lower limbs in a professional athlete.

Hierarchically designed nanocomposites for triboelectric nanogenerator toward biomechanical energy harvester and smart home system

Triboelectric nanogenerator (TENG) has realized broad application prospects in the internet of things, human-machine interfaces, artificial intelligence. Among the abundant material options, polymer-based nanocomposites are highly potential for triboelectric devices, owing to their flexibility, easy processing and especially tunable properties (dielectric constant, polarity, etc.) by various additives. At present, the widely used approaches for output performance enhancement of nanocomposite-based TENG are to boost the dielectric constant for improved charge storage ability and/or to enlarge the polarity difference of these triboelectric materials. Herein, we discovered that large amounts of dielectric additives would boost the dielectric constant while impair the triboelectric polarity of nanocomposites with degraded output performance. A hierarchical design strategy by additionally constructing a triboelectric coating on the high dielectric nanocomposites is proposed to balance the dielectric constant and triboelectric polarity of nanocomposites for enhanced triboelectric performance. The hierarchical nanocomposites possess a high dielectric constant (εr ~ 82.35 at 103 Hz) and optimized triboelectric polarity. Owing to the synergistic influence of dielectric incorporation and hierarchical design by triboelectric coating, an enhancement of short-circuit current density and maximum instantaneous power density by 4.1 and 23.1 times, respectively, are achieved. Theoretical mode of hierarchical nanocomposites is established to guide the design and optimization. A polymer dispersed liquid crystal film driven by TENG and its application in smart home system are demonstrated successfully. This work facilitates the exploration of multi-layered nanocomposite materials for high-performance TENG in biomechanical energy harvester and smart home system applications.

Solid-state intrinsically-superstretchable multifunctional nanogenerator fiber for biomechanical and ambient electromagnetic energy harvesting and self-powered sensing

Developing energy devices that are soft but tough and can extract multiple forms of surrounding energy is a crucial challenge for sustainable use of wearable electronics. Here, we report a solid-state naturally superstretchable (~590% stretchability) multifunctional nanogenerator fiber that can scavenge both biomechanical energy (e.g., from body motion) and dissipated electromagnetic energy (e.g., from nearby electrical appliances). Not only collect two types of waste energy, but also it can act as self-powered sensor. It comprises a conducting composite-coated extensible fiber clad in a triboelectric elastomer and extracts energy through triboelectrification (424 V m−1, 9.53 µA m−1, and ~85.2 µW m−1) and electromagnetic induced electrification ( ± 8.8 V m−1, ± 1.6 μA m−1, and ~2.81 μW m−1 at 60 Hz). The behavior to harvest nearby electromagnetic energy is successfully demonstrated in a carbon nanotubes (CNTs)-based composite. The collected energy can power electronic gadgets. Moreover, it can transmit biomechanical information, including physiological/respiratory signals, vibration of vocal cords, gestures, and touching, via self-generated electricity. The fibers are further used as self-powered human-machine interfaces in system-level smart clothing. The fiber that unites mechanical freedom and the ability of capturing multiple forms of energy and self-powered sensing can meet vast application needs for wearable/stretchable/personal energy and sensing technologies.

A triboelectric nanogenerator for mechanical energy harvesting and as self-powered pressure sensor

Recently, the development of triboelectric nanogenerators (TENGs) based on the natural material have aroused widespread concern. Here, we report a novel bamboo stick-based triboelectric nanogenerator (B-TENG) that can both harvest biomechanical energy and act as a self-powered pressure sensor. The polydimethylsiloxane (PDMS) layer and bamboo stick layer form the triboelectric layers, and the conductive copper is used as the conductive electrode. According to the results, the output power of B-TENG can achieve the maximum value (about 217.38 μW) and the internal resistance of B-TENG is 40 MΩ. Besides, the B-TENG can realize the open-circuit voltage (Voc) of 169.75 V and short-circuit current (Isc) of 3.6 μA, respectively. Furthermore, the B-TENG can also play the role of a self-powered pressure sensor to reflect the change of pressure. We believe this work will promote the development of TENG devices and self-powered sensor.

A large-area versatile textile for radiative warming and biomechanical energy harvesting

Both thermal management and electricity generation are becoming two basic functions for next-generation clothing integrated with wearable electronics. However, such versatile textiles with a simple design and great comfort have been rarely reported. Here, we propose a tri-layer textile that not only realizes solar and passive radiative warming but also harvests biomechanical energy to generate electricity. The textile is achieved by assembling photothermal nanoparticles on an infrared-reflective and conductive fabric with a tribo-negative polytetrafluoroethylene (PTFE) nanofiber membrane on the backside. The textile offers both a minimal thermal emissivity (down to 11.0%) and a maximum solar absorptivity (up to 83.7%), effectively suppressing radiation heat loss and boosting the harvested solar-thermal energy. Wearing such a textile enables a 3 °C drop of the indoor heating setpoint compared to a cotton textile, saving 25.2–100% of building energy consumption in ten cities worldwide. Moreover, the textile can serve as a single-electrode triboelectric nanogenerator. Remarkably high outputs (150–352 V, 7.5–27.8 μA) can be attained upon hand touching with different forces (14.7–44.0 N) and frequencies (0.9–3.9 Hz), which can power 41 LEDs. This textile opens a promising direction on how to develop a multifunctional energy-saving and electricity-generation textile while keeping thermal comfort for wearers.

A self-supported structure hybrid triboelectric/piezoelectric nanogenerator for bio-mechanical energy harvesting and pressure sensing

Recently, nanogenerators (NGs) based on triboelectric effect and piezoelectric effect have attracted worldwide attention. However, the development of NGs still faces many challenges, including reasonable structural design, multi-functional application, etc. Here, we reported a novel self-supported structure hybrid triboelectric/piezoelectric nanogenerator (TPNG) to harvest low-frequency and low amplitude mechanical energy through friction and deformation. The result of the experiment confirmed that the triboelectric part (size: 4 cm × 3 cm) of TPNG can achieve the maximum output power of 1.32 mW, and the piezoelectric section (size: 8 cm × 3 cm) of TPNG can arrive at 4.14 μW. Moreover, the triboelectric transferred charges and piezoelectric transferred charges of TPNG can get to 52.5 nC and 54 nC, respectively. In addition, all preparation materials are common commercial materials, which contributes to low-cost and large-scale production. The electrical energy produced by the TPNG device can drive 19 commercial light-emitting diodes (LEDs) and electronic calculators. The TPNG device can also serve as a self-powered sensor to reflect the change of pressure. This design realizes the integration of triboelectric devices and piezoelectric devices and will promote the development of self-powered flexible sensors.

Stretchable freezing-tolerant triboelectric nanogenerator and strain sensor based on transparent, long-term stable, and highly conductive gelatin-based organohydrogel

Conductive hydrogels have attracted tremendous attention for the next-generation electronic/energy/robotic application owing to their excellent mechanical and electrical properties, including stretchability, high conductivity, and stability. How to simultaneously realize their highly transparent, self-healing, antifreezing/antidrying, biocompatible and highly conductive features through a simple approach is still a challenge. Herein, the stretchable freezing-tolerant triboelectric nanogenerator (TENG) and strain sensor have been developed based on a transparent, long-term stable, and highly conductive gelatin/NaCl organohydrogel (GNOH), which is prepared via a facile immersion strategy in a glycerol/water binary solvent. The GNOH demonstrates superior merits of strain (300%), transparency (85%), high conductivity (1.6 S/m), freezing tolerance (−20 ℃), self-healing capability (91%), and environment stability (over 30 days). Furthermore, the wearable strain sensors enable the detecting, quantifying, and monitoring of human activities with high sensitivity of about 2.5 (strain of 0–200%). Meanwhile, the fabricated TENG in single-electrode mode can achieve excellent electrical outputs to power portable electronics when efficiently harvesting biomechanical energies, even at harsh cold temperature (−20 ℃). Additionally, a flexible self-powered calculator based on the arrayed TENG as touch panel is also explored for human-machine interaction (HMI). This study paves the way for potential applications in wearable electronics, healthcare monitoring, biomechanical energy harvesting and HMI.

Single-electrode mode TENG using ferromagnetic NiO-Ti based nanocomposite for effective energy harvesting

This work presents the mechanochemical synthesis of ferromagnetic NiO-Ti-based nanocomposites and exploits them as a positive triboelectric layer to enhance the performance of a triboelectric nanogenerator (TENG). Magnetization and charge polarization play crucial roles in augmenting the triboelectric performance. Various physicochemical properties, such as structure, morphology, surface topology, and magnetic properties of nanocomposites, are presented. The fabricated single-electrode (SE) operating mode TENG device generates a voltage of 62 V and a current of 250nA. SE-TENG can power up low-power electronics such as a wristwatch and LEDs and harvest biomechanical energy from breathing (inhale and exhale) during standing, sitting, and bending positions.

Metal-organic framework-derived nanoporous carbon incorporated nanofibers for high-performance triboelectric nanogenerators and self-powered sensors

Metal-organic frameworks (MOFs), which are highly crystalline materials, possess several intriguing properties but have remained largely unexplored for triboelectric nanogenerators (TENGs). Herein, MOF-derived cobalt-based nanoporous carbon (Co-NPC) incorporated polyvinylidene fluoride (PVDF) composite nanofibers (NFs) are proposed as a highly electronegative tribomaterial for boosting the performance of TENGs in the mechanical energy harvesting applications. Co-NPC, with a high surface area and excellent nanoporosity, greatly improved the electroactive β-phase formation and the dielectric constant of the PVDF composite NFs. As a result, the surface potential and charge trapping capability of the composite NFs increased by 4 and 9.5 times, respectively, resulting in a significant enhancement of the TENG performance. The as-fabricated Co-NPC/PVDF NF-based TENG (CNP-TENG) showed an excellent power density (19.24 Wm-2) and sustainably powered small electronics by harvesting biomechanical energy. The CNP-TENG exhibited excellent output performance at 95% relative humidity (RH) and exhibited stable output for long-term operations (> 60k cycles). Besides energy harvesting, the CNP-TENG was demonstrated as a self-powered pressure sensor with ultra-high sensitivity of 6.39 V/kPa that applied for diverse motion sensing and smart home control system applications. This study successfully introduced MOF-derived nanomaterials to enhance the energy harvesting performance of TENG which paved the way for a new pool of tribomaterials.

The benefits of combining 1D and 3D nanofillers in a piezocomposite nanogenerator for biomechanical energy harvesting.

Mechanical energy harvesting using piezoelectric nanogenerators (PNGs) offers an attractive solution for driving low-power portable devices and self-powered electronic systems. Here, we designed an eco-friendly and flexible piezocomposite nanogenerator (c-PNG) based on H2(Zr0.1Ti0.9)3O7 nanowires (HZTO-nw) and Ba0.85Ca0.15Zr0.10Ti0.90O3 multipods (BCZT-mp) as fillers and polylactic acid (PLA) as a biodegradable polymer matrix. The effects of the applied stress amplitude, frequency and pressing duration on the electric outputs in the piezocomposite nanogenerator (c-PNG) device were investigated by simultaneous recording of the mechanical input and the electrical outputs. The fabricated c-PNG shows a maximum output voltage, current and volumetric power density of 11.5 V, 0.6 μA and 9.2 mW cm-3, respectively, under cyclic finger imparting. A high-pressure sensitivity of 0.86 V kPa-1 (equivalent to 3.6 V N-1) and fast response time of 45 ms were obtained in the dynamic pressure sensing. Besides this, the c-PNG demonstrates high-stability and durability of the electrical outputs for around three months, and can drive commercial electronics (charging capacitor, glowing light-emitting diodes and powering a calculator). Multi-physics simulations indicate that the presence of BCZT-mp is crucial in enhancing the piezoelectric response of the c-PNG. Accordingly, this work reveals that combining 1D and 3D fillers in a polymer composite-based PNG could be beneficial in improving the mechanical energy harvesting performances in flexible piezoelectric nanogenerators for application in electronic skin and wearable devices.

Customizing Triboelectric Nanogenerator on Everyday Clothes by Screen-Printing Technology for Biomechanical Energy Harvesting and Human-Interactive Applications

Customizing Triboelectric Nanogenerator on Everyday Clothes by Screen-Printing Technology for Biomechanical Energy Harvesting and Human-Interactive Applications